Process for producing regenerated cellulose articles from viscose



Jan. 33,1953 G. A. RICHTER, JR., ET AL 2,625,461

PROCESS FOR PRODUCING REGENERATKED CELLULOSE ARTICLES FROM VISCOSE Filed oct. z. 195o A INVENToRs. v @EQRRE ALV/N R/cHR,./n.

R/CHAR@ H BRAUNUCH Patented Jan. 1.3, 1.953

PROCESS FOR PRODUCING REGENERATEp .cELLULosE .ARTICLES FRoMvrsoosE IGeorge A. Richter, Jr., Springiielmand Richard H."raunlich, West Chester, Pa., 'assig'nors ,to American Viscose Corporation, Wilmington,

,11d-4 @integrative vf Delaware vzfiilriicauf;,n october 2, 195o, serial No. I187,358 zo Claims. (c l. l11s- 54) This inventiontrelatesto the manufacture Aof articial filaments .and fibers. from viscose. lMore particularlvit .relates to a noveltwoestage spinning process for the production of regenerated cellulosebers. By the term two-stage spinning is meant that type of process in which the viscose is first coagulatedwith little or noregeneraton ,and this isffollow'ed .by .asubsequent stage of regeneration.

This application is Ea continuation in part .of our application, SerialfNo. 128,382, filed November 19, 1949, entitled .VProcess for Producing .Regenerated Cellulosenrticles From vViscosefnow abandoned.

It has been recognized in the patent and `technical literature thatvarticial `filaments `can vbe formed by spinning viscose into a bath containing phosphate ions. Eorrexam'ple, iflviscose is spun into a coagulating bathv containing. sodium phosphates land .sodium `-sulfate, cellulose .Xanthate threads areobtainedwhichcan thenbe stretched and treated. with amedium iorhydrolyzing'cellulose xanthate to cellulose'. This constitutes what is known asa two-stage process." How.- ever, while such1 twofsta'gepr'ocedures have been known, they haveremained more or less laboratory Curiosities due to their high -cost 'and impractcality. In such previously known systems, al1 of the sodium hydroxideventering the system with the viscosehas generally beenneutralized by phosphate salts or phosphoric acidjw'hich are prohibitively expensiye as compared to the sulfurie acid which is used as theneutralization agent in conventional viscose spinning in which coagulation and regeneration are performed in Aa single step in a single bath.` A separaterecovery system for phosphoricacid or phosphate salts would be necessary,lbutthe added expense vrand trouble therebyl .entailed prevents the products obtained by such vsystems trom bcoming'com petitive withthose from fthe singlestage sulfuric acid systems from the standpoint of cost.

One object ofx thisinyention .is yto providea simple, readily controllabla.economically feasible, continuous twogstagenphosphate system for producing'nbers from viscose.

Bythe l present invention,` the vclisadvantages which formerly attended-the" execution of the twostage phosphate process are eliminated-*because the coagulating bath containing the phosphoric acid .and/or sodium phosphates, and-the'regenerating bath, are integrated.,into av simple, practical, economicalfand vnoyel .two-stage. system in which a phosphate-*n.bath serv-es V todeliydrate the viscose lament-formng streams andas a vehicle to carry hydrogen ions to the yiscose filamentforming streams :ion neutralizing'-the sodium hydroxide thereof, thereby Acoagulating them, l iand the phosphate bath is maintained at, or lrecon verted to, its initialcoagulating effectivenessby the .addition of sulfuric acid to the two-stage systemiV -Ineiectlit is the sulfuric acid that is consumed yfor the neutralization of virtually al1 of thefsodium hydroxide in the viscose.

The invention 'will be described with reference tothe accompanying drawing, in which Fig. 1 illustrates schematically the ,flow of `various Streams throughtheSyStem;

Fig'. 2 is adiagramlnatic elevation of apparatus suitable for usein practicing one embodiment of .themvention;

Fig3 is a diagrammatic elevationof apparatus suitable for use inpractijcing another embodiment 0f the invention; and

Fig Y4 is a diagrammatic elevation .of .apparatus suitable for use 1inipracticn`gja fiuztherl einlbodimentof the invention.

vIn Fig. 1 ofthe drawing, A represents the storageand Amake-up .tank fortthe. coagulating bath vjwhichtcomp'nrises an aqueouspsolutidn of sodium su1fateanldanacid sodium phosphate and which mayalso contain phosphoric v,acid,j,and B represents thevessel into which. theyivscoseis spun. The coagulating' bath ismeirculated between tank vAand vessel vB vin streams, 9r and I 0. "Crepresents the` storage and make-,up lankior .theiregenerating bath, the compositienjfwmch is discussed below., and Drepresenlts .thevessel Ycontaining regenerating bath throughfwhich .the coagulated cellulos'eQxanthate thread is passed vtorin'itiate rapid regenerationof the cellulose. The regen.- erating. bathjis circulated b'etweentank .C and vesselDin streams yIl and vI2.

In accordanpe with .the broader aspects .of the invermion,v viscose' letream l2 in rig; 1") is extruded througha vspinneret r2l) intothe ycoagulating bathA in vessel B. The bundle of' cellulose xanthate ilanfientsI ,thus` vformed' is drawn from the, coagulating bath; stripped vof ,excess coagulating bath, and passedthro'ugh.aregenerating bath containedin vessel 1D; After the thread is Withdrawn v from vessel .,D, itl preferably passes through a strippingdevice and 'out of .the system `(stream ,4) and f y be then desulded, bleached, washed, treated with 'a,nish.,dried,` and collected 1n continuous manner; Iifdesire'd, it may be cut into staple fiber before or after these liquid-'treating and drying steps.

` Ifl desired, nostretch.needbeperformed on the filaments except hat ,which would." ocu'r bett/n the jet and first drawgqfry enge, butffof'mo'st purposes, a `stretch of. at Vleas fil) ,v, and vpreferably @200% or ,more; 1siapp1edafterthe thread leaves .the coagulatmgf bath'. The nia- 3 ments or threads may be stretched between the coagulating and regenerating bath, as they enter the regenerating bath or as they are passed through the regenerating bath. k

In the preferred. embodiment,` the coagulated cellulose xanthate iilaments are stretched between the coagulating and regenerating baths and relaxed during their passage through the regenerating bath so that regeneration of the cellulose is effected while the filaments are relaxed. Such filaments are less brittle and more readily workable on conventional textile Working equipment than the filaments which are stretched simultaneously with regeneration.

Apparatus for carrying out the preferred embodiment is shown in Fig. 2. Referring to Fig. 2, the coagulated cellulose xanthate filaments are shown proceeding from the coagulatingl bath contained in vessel B over the guide 22, to the godet 23 and thence to godet 38. As they proceed from godet 2S to godet 32. the filaments are passed between stripping guides 24 and 25 arranged in staggered relation to strip excess coagulating liquid therefrom. Between godets 23 and 30, the filaments are stretched to the desired extent. The stretched filaments proceed from godet 3U and through the regenerating bath contained in vessel D, and are withdrawn from the regenerating bath over the guide 21, and passed between the stripping 'guides 28, 29 arranged in staggered relation to strip excess regenerating liquid from the filaments, and thence to the godet 3|. From godet 3l the thread passes out of the system (stream 4) and may then be desulded, bleached, washed, treated with a iinish, dried, and collected in continuous manner; if desired, it may be out into staple fiber before or after these liquid-treating and drying steps.

In order to insure relaxation of the filaments in the yarn or tow during regeneration of the cellulose in vessel D, godet 3i is driven at a lower peripheral speed than godet 30. Generally, the peripheral speed of godet 3| (linear speed of yarn) is from 1 to 3% slower than that of godet 3U, the thread being relaxed from 1 to 3% as it passes through the regenerating bath. The thread can be relaxed more than 3% during passage thereof through the regenerating bathcontained in vessel D, if desired.

In the embodiment shown in Fig. 3 of the draw-A ing, the thread is stretched simultaneously with regeneration of the cellulose. As shown, the thread is withdrawn from` the coagulating bath in vessel B over the guide 22 to godet 23 (godet 38 is omitted in this modification of t-he invention) and passes between the stripping guides 2r! and 25 arranged in staggered relation. From guides 24 and 25, the filaments pass into and through the regenerating bath in vessel D, and

-are withdrawn from the regenerating bath over guide 21, and passed between the stripping guides 28 and 29, to the godet 3l.

In order to stretch the thread to the desired extent as it is passed through the 'regenerating bath, godet 3l is driven at a higher peripheral speed than godet 23. From godet 3l the thread passes out of the system (stream 4) to the aftertreating stages as referred to in connection with Fig. 1.

In the several embodiments hereinabove the jet-velocity: draw-off ratio may have any of the conventional values, such as 1:3 to 1:03. I-Iowever, for special purposes ratios outside this range may be used. For example, the process of this invention is` adaptable .to the production of crimped regenerated cellulose filaments by methods involving the spinning of viscose with an exceptionally high jet-velocity: draw-olf ratio. Such crimped filaments can be obtained by extruding the viscose into a phosphate coagulating bath as disclosed herein at a high velocity of extrusion, withdrawing the coagulated cellulose xanthate filaments at a low velocity of draw-off, stretching the coagulated xanthate filaments at least 25% over their straight length (i. e. to 125% of their original length), and regenerating and drying the stretched filaments in a relaxed condition. The velocity of extrusion of the viscose into the phosphate coagulating bath is preferl ably at least four times the velocity of draw-off.

Apparatus suitable for use in practicing the last-.mentioned embodiment of the invention is shown in Fig. 4. Referring to Fig. 4, the viscose lament-forming composition is forced through the spinneret 2D into the phosphate coagulating bath contained'in vessel B under suiicient pressure that the velocity of extrusionv of the filaments is at least four times the velocity of drawoif by the godet 23. The filamentous solution buckles and bends as it is forced into the coagulating bath in Vessel B, thus forming highly crimped filaments of cellulose xanthate. The filaments are withdrawn from vessel B over the guide 22 by the godet 23 and passed to godet 38 between the stripping guides 24 and 25. Godet 30 is driven at a higher peripheral speed than godet 23, whereby the filaments are stretched at least 25% over their straight length. From godet 30, the filaments drop into and through the regenerating bath contained in vessel D from which they are withdrawn over guide 21 and passed to godet 3l between the staggered stripping guides 28 and 29. Godet 3l is -driven at a lower peripheral speed than godet 3B, so that the nia-ments dropped into vessel D tend to pile up on one side of the partition 32 which extends to within a short distance of the bottom wall of the vessel. Thev filaments pass under the partition, and under the guide A33 submerged in the regenerating bath, the regeneration thus being effected while the filaments, yarn, or tow are in a relaxed condition. Thethread .leaves the system (stream 4) and proceeds to the after-treating stages. It may be after-treated, i. e., purified and washed inrelaxed condition, or under tension, but in any case it is dried in the relaxed condition to permit the free formation of crimp.

This invention is concerned more particularly with the manner in which the non-cellulosic portions of streams 2 to i9 (Fig. l) are manipulated, and especially with the reactions resulting in the consumption of sulfuric acid exclusively for the neutralization of the sodium hydroxide introduced into the system with the viscose.

In the present process', the coagulating bath may have a pH of 1.5' tolO. When operated in the pH range of 3.7 to 9 in the coagulating bath, the sodium hydroxide reacts with mono-basic sodium phosphate obtained by the reaction of sulfuric acid with dibasic sodium phosphate, the monoand di-basic sodium phosphates being continuously reversibly converted in the system from one to the other.

Thus, when the viscose is introduced into the coagulating bath containing mono-basic sodium phosphate, the sodium hydroxide reacts with the mono-basic sodium phosphate according to the following reaction:

' The amount of solution carried by the thread in stream 3 into the regenerating bath and the amount of sulfuric acid in stream '6 may be correlated so that when-all of the excess regenerating bath is cycled back to tank A by stream 1, no additional sulfuric acid need be added to the coagulating bath and stream 8 may be omitted. The preferred system involves stripping of stream 3 to minimize loss of phosphate in stream Il.

As previously noted, the coagulating bath comprises an aqueous solution of sodium sulfate and sodium phosphates, and may also contain phosphorc acid.' Some latitude in the actual composition of the bath is permissible, so long as the acid in the overflow from the regenerating bath storage tank C to tank'A (stream l) does not overcompensate for the sodium hydroxide entering the system with the viscose. The coagulating bath has a pH of 1.5 to 10 and contains phosphate radicals in a selected proportion between 5 and 20% by weight, and sodium sulfate in a selected proportion between 5 and 20%, by weight, the conditions selected being maintained throughout the spinning. The temperature of the coagulating bath maybe room temperature or higher and is preferably between 45 and 55 C. The immersion length for the fibers in the coagulating bath is not critical, and may-be, for instance, between 12 and 20 inches. v

When the concentrations of sodium sulfate and phosphate radicals in the coagulating bath are kept within the ranges just specined and the ratio of solution to cellulose in stream 3 is not greater thanl 8:1, the sulfuricacid content of the regenerating bath may be maintained at about 1 to by weight and preferably 3 to 6%, and the equilibrium values for phosphoric acid and sodium sulfate in the regenerating bath are 5 to l() and 10to 20%, respectively. The regenerating bath may have room temperature or higher and preferably has a temperature of from 45 to V The viscose may be a normal viscose that is, it may have a'salt point of 3 to 6 (sodium chloride salt test value), a cellulose content of from 6 to 9%, and a sodium hydroxide content of from 6 to 9%. The viscosity may be normal, also, that is between 30Y and 60 seconds as measured by the ball fall test; However, it is preferred to use a viscose of higher viscosity, for example, one having a ball fall viscosity of 65 to 120 seconds, and, consequently, a higher degree of polymerization. Such viscoses are obtained by reducing the storage time of the soda cellulose crumbs, as is well known. The cellulose usedvin making the viscose may be of cotton or wood origin or any mixture of the two.

The fibers leaving the regenerating bath are sent directly to the usual nishing stages through which regenerated cellulose bers are passed in the vnormal course of their production.

The bersexhibithigh tensile strengths (wet and dry) combined with low extensibilities (wet and dry) and low swellings (cross-sectional and linear) upon exposure to water or water vapor. Average fiber properties are tabulated below:

Tenacity (dry) 3.3 to 4.5 grams/denier Tenacity (wet) 2.0 to 3.0 grams/denier nxtensihiuty (dry) '1.o to 8.5% Extensibility (wet) 7.0 to 8.0% Cross-sectional swelling- 40% Linear swelling 0.25%

Youngs modulus (WSU-.- F

8 In the following examples, specific embodiments of the novel two-stage process of the invention are described with reference to the figures of the drawing designated.

Erample I A 100 cotton viscose having a sodium chloride salt test value of 6 i 0.5, a ball fall viscosity of 75 seconds at 21 C. (soda cellulose storage time at 21 C.: 36 hours), and containing '7.8% cellulose, 33% CS2 (based on the cellulose), and 6.6% sodium hydroxide was pumped through a spinneret 20 containing 980 orifices, each 0.0025 inch in diameter, into an aqueous coagulating bath contained in vessel B in the system of Figures 1 and 3, and comprising a solution containing, by weight 11.9 i 0.5% phosphate radicals (as monoand di-sodium phosphates) and 10.0 i 1.0% sodium sulfate at a pH of 5.0 :L 0.2 and a temperature of 50 C. After an immersion of 12 inches, the cellulose xanthate filaments were withdrawn from the bath over guide 22, lapped around godet 23, passed through vessel D containing the regenerating bath (immersion distance: 30 inches), withdrawn over the guide 21 between the stripping guides 28 and 29, arranged in staggered relation beyond the regenerating bath to strip the fibers of excess solution, to the godet 3|. The solution stripped from. the yarn tow between guides 24 and 25, and guides 28 and 29 was returned to the coagulating and regenerating baths respectively in streams I8 and I9, as shown in Fig. 1. The fibers advancing from the coagulating bath contain approximately ten pounds of coagulating liquid per pound of cellulose. After stripping by the staggered guides 24 and 25, the fibers contained approximately seven pounds of coagulating liquid per pound of cellulose. The fibers were stretched 210% between godets 23 and 3l. The spinning speed at godet 3| was 60 meters per minute.

Initially the regenerating bath, which was maintained at 50 C., consisted of water containing 5% sulfuric acid, 7% phosphoric acid and 18% sodium sulfate. These are the equilibrium values for phosphoric acid and sodium sulfate as calculated from analysis data on the cellulose xanthate thread (stream 3 of Figure 1) after stripping thereof between guides 24, 25, and on the cellulose thread (stream 4 of Figure 1) after stripping thereof by the guides 28 and 29. The regenerating bath volume was kept constant by replacing water lost by evaporation and returningl the overflow (stream 1 of Figure 1) to the coagulating bath at the rate of 2.4 lbs. per pound of bone dry yarn produced. This overflow from the regenerating bath to the coagulating bath assists in maintaining the coagulating bath composition and pH constant. However, in addition to the reagents cycled from the regenerating bath to the coagulating bath, the coagulating bath was intermittently fortified by the addition of 4.3 lbs of 94% sulfuric acid (stream 8 of Figure 1) at regular six-hour intervals (0.33 1b. of sulfuric acid per pound of bone dry yarn produced) and 5.9 lbs. of phosphoric acid (stream 9a of Figure 1) at regular six-hour intervals `(0x12 lb. of phosphoric acid per pound of bone dry yarn produced). Nine pounds of 94% sulfuric acid were added to the regenerating bath in tank C (stream 8 of Figure 1) at regular 12 hour intervals (0.73 lb. of sulfuric acid per pound of bone-dry yarn produced) to maintain the concentration of free sulfuric acid in th regenerating bath at5%; f

The concentrations of sodium sulfate an phosphoric acid in thel regencrat-ingl bath, cal culated as equilibrium values at the start', remained substantially constant. The coagulatingbath was drawn ofi` 'intermittently to a vacuum crystallizer K (Figure 1) for crystallization of theA excess sodium sulfate accumulated in the system. The excess water built up in the system was evaporated in evaporator E` (FigureA 1) The nbers, after the usual after-treatments in,- cluding desulding, bleaching, washing and drying, were highly crystalline as shown by X'ray and hydrolysis rate studies. The dry and wet tenacities of the be'rs were 4.3 gms/denierand 2.6 gms/denier, respectively. The dry and. wet extensibilities were 8.7% and 9.5%, respectively. The cross-sectional swelling is in the range of 40 to- 45%; linear swelling about 0.25%

Example. Il

Example I is repeated, using,A the system of Figures 1 and 2 of the drawing. The viscose was; pumped into the coagulating bath in vessel B, withdrawn over the guide 22, lapped around godet 23, passed to godet 30 between the stripping guides 24 and 2,5 and stretched 102 between the godets. From godet 30, the yarn comprisingthe cellulose xanthate filaments was passed through vessel D containing the regenerating bath (immersion distance: 30 inches), withdraw-n over the guide 21, and passed between the stripping guides 28 and 29 to godet 3|. Godet 3| was driven at a peripheral speed such that during passage of the filaments through the regenerating liquid in vessel D they were relaxed 3%. A yarn producedy as described in this example had the following properties:

Total denier 1572 Denier/iilament 1.61 Tenacity in gms/denier:

Dry 3.4 Wet 2.0 Extensibility:

Percent Dry .--i 8.5 Wet 8.0

The yarn cr filaments were found to be less brittle than the laments or yarn of Example I.

Example III.

Example Il was repeated using the system of Figs. 1 and 4. The viscose was extruded into the coagulating bath in vessel B at an extrusion velocity four times greater than the rate at which the Iiilamerits were withdrawn from the bath by godet 23. The iilaments were stretched 125% between godets 23 and 3Q and allowed to fall into the regenerating bath contained in vessel D. The filaments passed under the partition 32 and the guide roll 33, and were withdrawn from the regenerating bath over the guide 21, and passed between 4the stripping guides 28 and 29 to godet 3l. Godet 3i was driven at a lower speed than godet 30, to permit free relaxation of the filaments during their passage through the regenerating bath. The filaments were then removed from the system (stream li of Fig. 1) and subjected to the usual after-treating liquids including desuliiding, bleaching, washing and drying. These liquid Aaf ter-treatments andthe drying were performed while the yarn comprising theiilaments waslin skein form and free to relax. Crimped filaments or yarn are obtained by this process.

Sonie modification of the eoagulating bathis permissible. Thus, a small proportion of .a surface-active agent which is inert to` the constituents of the bath may be 'addedforA preventing spinneret incrustation.

If desired, in carrying out this process, the viscose may be extruded into the coagulating bath in vessel B in a pulsating manner, i. e., the viscose maybe delivered to the spinneret at a varying rate to produce filaments -having irregular denier along their length, sections along the lamcnt of heavier denier, which may be called nubs or slubs" alternating with sections of lighter denier. Such irregular filaments may have particular advantages. Examples of apparatus suitable for-varying the rate of delivery of the viscose to the spinneret, to produce the filaments ci irregular denier, are shown in U. S. Patents Nos. 2,142,597 and 2,065,124.

By the continuous two-bath process of the invention the fibers are produced at substantially no increase in cost as compared to the cost ofi manufacturing regenerated cellulose fibers by conventional procedures utilizing a single coagulatingy and regenerating bath. sulfuric acid is consumed for neutralizing substantiallyl all of the sodium hydroxide introduced into the coagulating bath; the phosphate radicals are c-irculated in the system and serve as a vehicle for the hydrogen ions derived from the sulfuric acid, the only loss being a small one incidental to removal of the phosphate radicals from the regenerating bath with the yarn, which maybe recovered if desired; there is substantially no mechanical loss of s ulfui-ic acid by removal in stream 4, which contrib utes materially to the economical operation oi the process; ready control of all variables is possible; and the circulating system is entirely selfregulating.

In the embodiments of the invention which have been described in detail, sodium sulfate is used as the dehydrating agent in the coagulating bath throughout the spinning, and for reasons of economy and simplicity, this is preferred. However, other dehydrating agents which are useful in the coagulation of viscose may be present in the coagulating bath at the start, and preferably those dehydrating agents which are stable under the pH conditions existing in the coagulating bath and in the regenerating bath. Examples of other suitable dehydrating agents are sodium chloride and magnesium sulfate. During spinning, such agents are gradually replaced by sodium sulfate. Y

Since some variations may be made in the process as set forth in specic detail in the examples, it is to be understood that the invention is not to be limited except as defined in the appended claims.

1 A method for the production of Shaped arti.- cles of regenerated cellulose from viscose which comprises extruding viscose in to an aqueous c oagulating bath having a pH of 1.5 to 1 0 and containing a dehydrating agent for viscoseand inorganic phosphate .radicals at least someof. which are in the form of a sodium salt, withdrawing the cellulose xanthate article thus fori-ned from the bath, passing the cellulose xanthate article carrying adhering coagulating solution to and through an aqueous cellulose-regenerating bath comprising an equilibrium mixture of the dehydrating agent. ,and phosphoric acidi, and sulfuric acid to convert to phosphoric acid` at least part of the phosphate salts in the article,y stretching the artiolo .at somo time between coagulation and complete regeneration of the cellulose, continuously passing excess regenerating bath built up during the spinning to the coagulating bath in a controlled amount so correlated with the amount of coagulating solution carried into the regenerating bath by the cellulose xanthate article that the pH balance in the coagulating bath is not upset, and removing from the coagulating bath by evaporation and crystallization water and sodium sulfate built up in said bath during the extrusion of the viscose, the composition and pH of the coagulating bath being maintained substantially constant from the beginning to the end of the extrusion.

2. A method for the production of shaped articles of regenerated cellulose from viscose which comprises extruding viscose into an aqueous coagulating bath having a pH of 1.5 to and containing sodium sulfate and inorganic phosphate radicals at least some of which are in the form of a sodium salt, withdrawing the cellulose xanthate article thus'formed from the bath, passing the cellulose xanthate article carrying adhering coagulating solution to and through an aqueous cellulose-regenerating"bath comprising an equilibrium mixture of sodium sulfate and phosphoric acid, and sulfuric acid to convert to phosphoric acid at least part of the phosphate salts in the article, stretching the article at some time between coagulation and complete regeneration of the cellulose, continuously passing excess regenerating bath built up during the spinning to the coagulating bath in a controlled amount so correlated with the amount of coagulating solution carried into the regenerating bath by the cellulose xanthate that the pH balance in the coagulating bath is not upset, and removing from the coagulating bath by evaporation and crystallization water and sodium sulfate built up in said bath during the extrusion of the viscose, the composition and pH of the coagulating bath being maintained substantially constant from the beginning to the end of the extrusion.

3. A method for the production of shaped articles of regenerated cellulose from viscose which comprises extruding viscose into an aqueous coagulating bath having a pH of 1.5 to 10 and oontaining phosphate radicals atleast some of which are in the form of a sodium salt, withdrawing the cellulose xanthate article thus formed from the bath, passing the cellulose xanthate article comprising adhering coagulatlng solution to and through an aqueous cellulose-regenerating bath comprising an equilibrium mixture of sodium sulfate and phosphoric acid, and sulfuric acid to convert to phosphoric acid at least part of the phosphate salts in the article, stretching the article at some time between coagulation and complete regeneration of the cellulose, continuously passing excess regenerating bath built up during the spinning to the coagulating bath in a controlled amount so correlated with the amount of coagulating solution carried by the article into the regenerating bath that the pH balance in the coagulating bath is not upset, adding to the coagulating bath predetermined amounts of sulfuric and phosphoric acids from a source other than the regenerating bath, and removing from the coagulating bath by evaporation and crystallizaticn water and sodium sulfate built up in said bath during extrusion of the viscose, the composition and pH of the coagulating bath being maintained constant from the beginning to truding viscose through a spinneret into an aqueous coagulating bath having a pH from 1.5 to 10 and containing sodium sulfate and inorganic phosphate radicals at least some of which are in the form of a sodium salt, withdrawing the cellulose xanthate fibers thus formed from the bath, passing the cellulose xanthate fibers carrying adhering coagulating solution to and through an aqueous cellulose-regenerating bath comprising an equilibrium mixture of sodium sulfate and phosphoric acid, and sulfuric acid to convert to phosphoric acid at least part of the phosphate salts in the iibers, stretching the fibers at some time between coagulation and complete regeneration of the cellulose, continuously passing excess regenerating bath built up during the spinning to the coagulating bath in a controlled amount so correlated with the amount of coagulating solution carried by the ilbers into the regenerating bath that the pH balance in the coagulating bath is not upset, supplementing the sulfuric acid and phosphoric acid introduced into the coagulating bath from the regenerating bath with predetermined amounts of sulfuric and phosphoric acids from a source other than the regenerating bath, removing from the coagulating bath by evapora-` tion and crystallization water and sodium sulfate built up in said bath during extrusion of the viscose, the composition and pH of the coagulating bath being maintained substantially constant from the beginning to the end of the extrusion, withdrawing. the fibers from the regenerating bath, after-treating the bers, and drying the iibers. l

5. A method as in claim 1, in which the cellulose xanthate articles are stretched between the coagulating bath and the aqueous cellulose-regenerating bath and relaxed during passage thereof through the regenerating bath.

6. A method as in claim 1 in which the cellulose xanthate articles are stretched as they are passed through the aqueous cellulose-regenerating bath.

7. A method as in claim 2, in which the cellulose xanthate article carries adhering coagulating solution in an amount oi' not more than 8 parts by weight of solution per part of cellulose into the regenerating bath, and all of the excess regenerating bath produced during the spinning operation is passed continuously to the coagulating bath.

8. A method as in claim 2, in which the viscose has a ball fall viscosity of from 65 to 120 seconds.

9. A method as in claim 2, wherein the coagulating bath contains, by Weight, from 5 to 20% phosphate radicals, from 5 to 22% sodium sulfate, and has a pH from 1.5 to l0.

l0. A method as inclaim 3, in which the cellulose xanthate articles are stretched between the coagulating bath and the aqueous cellulose-regenerating bath, and relaxed during passage thereof through the regenerating bath.

1l. A method as in claim 3, in which the cellulose xanthate articles are stretched as they are passed through the aqueous cellulose-regenerating bath.

l2, A method as in claim 3, in which the cellulose xanthate article leaving the coagulating bath is stripped of adhering coagulating solution to sucha extent that not more than 8 parts by weight of solution from the coagulating bath per part of cellulose are carried with the article into the regenerating bath, and all of the excess regenerating bath produced during the spinning.

operation is passed continuously to the coagulating bath.

13. A method as in claim 3, wherein the viscose has a ball fall viscosity of from 65 to 120 seconds.

14. A method as in claim 3, wherein the coagulating bath contains, by Weight, from 5 to 20% phosphate radicals, from 5 to 22% sodium sulfate, and has a DH from 1.5 to 10.

15. A method as in claim 4, wherein the I'lbers are stretched between the coagulating bath and 10 the regenerating bath, and relaxed during passage thereof through the regenerating bath.

16. A method as in claim 4, wherein the fibers are stretched as they enter the regenerating bath.

17. A method as in claim 4, wherein the bers l5 are stretched as they are passed through the regenerating bath.

18. A method as in claim 4, wherein the bers are stretched at least 40%.

19. A method as in claim 4, wherein the fibers are given a stretch of from 100% to 200%.

14 20. A method as in claim 4, wherein the viscose is extruded into the coagulating bath at an extrusion rate of at least four times the Velocity of draw-oi, stretched between the coagulatng bath and the aqueous cellulose-regenerating bath, relaxed during passage thereof through the regenerating bath, withdrawn from the regenerating bath, after-treated, anddried in relaxed condition.

GEORGE A. RICHTER, JR. RICHARD H. BRAUNLICH.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,236,648 Nagel et al. Apr. 1, 1941 20 2,512,968 Ray June 27, 1950 

1. A METHOD FOR THE PRODUCTION OF SHAPED ARTICLES OF REGENERATED CELLULOSE FROM VISCOSE WHICH COMPRISES EXTRUDING VISCOSE INTO AN AQUEOUS COAGULATING BATH HAVING A PH OF 1.5 TO 10 AND CONTAINING A DEHYDRATING AGENT FOR VISCOSE AND INORGANIC PHOSPHATE RADICALS AT LEAST SOME OF WHICH ARE IN THE FORM OF A SODIUM SALT, WITHDRAWING THE CELLULOSE XANTHATE ARTICLE THUS FORMED FROM THE BATH, PASSING THE CELLULOSE XANTHATE ARTICLE CARRYING ADHERING COAGULATING SOLUTION TO AND THROUGH AN AQUEOUS CELLULOSE-REGENERATING BATH COMPRISING AN EQUILIBRIUM MIXTURE OF THE DEHYDRATING AGENT AND PHOSPHORIC ACID, AND SULFURIC ACID TO CONVERT TO PHOSPHORIC ACID AT LEAST PART OF THE PHOSPHATE SALTS IN THE ARTICLE, STRETCHING THE ARTICLE AT SOME TIME BETWEEN COAGULATION AND COMPLETE REGENERATION OF THE CELLULOSE CONTINUOUSLY PASSING EXCESS REGENERATING BATH BUILT UP DURING THE SPINNING TO THE COAGULATING BATH IN A CONTROLLED AMOUNT SO CORRELATED WITH THE AMOUNT OF COAGULATING SOLUTION CARRIED INTO THE REGENERATING BATH BY THE CELLULOSE XANTHATE ARTICLE THAT THE PH BALANCE IN THE COAGULATING BATH IS NOT UPSET, AND REMOVING FROM THE COAGULATING BATH BY EVAPORATION AND CRYSTALLIZATION WATER AND SODIUM SULFATE BUILT UP IN SAID BATH DURING THE EXTRUSION OF THE VISCOSE, THE COMPOSITION AND PH OF THE COAGULATING BATH BEING MAINTAINED SUBSTANTIALLY CONSTANT FROM THE BEGINNING TO THE END OF THE EXTRUSION. 